On Wed, Apr 28, 2021 at 7:57 AM H.J. Lu [off-list ref] wrote:

On Wed, Apr 28, 2021 at 7:52 AM Andy Lutomirski [off-list ref] wrote:

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On Wed, Apr 28, 2021 at 7:48 AM David Laight [off-list ref] wrote:

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From: Yu-cheng Yu

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Sent: 27 April 2021 21:47

Control-flow Enforcement (CET) is a new Intel processor feature that blocks
return/jump-oriented programming attacks.  Details are in "Intel 64 and
IA-32 Architectures Software Developer's Manual" [1].

...

Does this feature require that 'binary blobs' for out of tree drivers
be compiled by a version of gcc that adds the ENDBRA instructions?

If enabled for userspace, what happens if an old .so is dynamically
loaded?

CET will be disabled by ld.so in this case.

What if a program starts a thread and then dlopens a legacy .so?

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Or do all userspace programs and libraries have to have been compiled
with the ENDBRA instructions?

Correct.  ld and ld.so check this.

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If you believe that the userspace tooling for the legacy IBT table
actually works, then it should just work.  Yu-cheng, etc: how well
tested is it?

Legacy IBT bitmap isn't unused since it doesn't cover legacy codes
generated by legacy JITs.

How does ld.so decide whether a legacy JIT is in use?